Field of the Invention
The present invention relates to a sheet feeding device that conveys a sheet to a predetermined position by separating and feeding sheets one by one, and an image forming apparatus that includes the sheet feeding device. For example, the present invention relates to a sheet feeding device applicable to an image forming apparatus such as a copying machine or a laser beam printer.
Description of the Related Art
A sheet feeding device feeds the sheets placed on a sheet feeding tray to the inside thereof through a pick-up roller and a conveyance roller.
In a case where a bundle of sheets is to be consecutively fed, separation unit is used. The separation unit separates the sheets fed by the pick-up roller, one by one by using a separation roller or a separation pad, and conveys the sheet to the inside of the sheet feeding device. The separation roller is pressed against and brought into contact with a conveyance roller, so as to be rotated and driven in a direction opposite to the sheet conveyance direction through a torque limiter. Further, the separation pad is pressed against the conveyance roller, and separates the sheets from each other with frictional resistance arising in a surface thereof. A pressure contact portion between the conveyance roller and the separation roller (separation pad) is referred to as a separation nip portion.
When a bundle of sheets is to be consecutively fed, a leading end of the sheet may be bent or damaged in a case where the leading end of the conveyed sheet is not fed to the separation nip portion or the leading end thereof is warped to cause a portion other than the leading end thereof to be fed into the separation nip portion. Therefore, it is essential to feed a sheet to the separation nip portion from the leading end thereof.
Japanese Patent Application Laid-Open No. 2008-68968 discusses a configuration in which a leading end of a sheet is smoothly guided to a separation nip portion through a swingable guiding plate that is arranged in parallel with a conveyance roller and supported by a rotating shaft disposed on a downstream side of the conveyance roller.
There is a demand in recent sheet feeding devices to support diversified sheet materials or a wider range of grammage. For example, although a range of supportable grammage has been 40 g/m2 to 130 g/m2 in the conventional technique, the range thereof is expanded to 30 g/m2 to 200 g/m or more.
In particular, because thin paper with a grammage of 42 g/m2 or less has low stiffness (hardness), behavior thereof is likely to be unstable when the thin paper is conveyed to a space on the upstream side of the separation nip portion.
Further, in recent sheet feeding devices, a number of sheets stackable on a sheet feeding tray tends to be increased in order to enable a large number of sheets to be conveyed by a single command. For example, although a number of stackable sheets has been 100 sheets in the conventional specification, the number thereof tends to be increased to 150 sheets to 200 sheets.
With respect to the sheet feeding device capable of stacking a large number of sheets, because a sheet bundle thickness in a maximum stacked state is increased, a height of the sheet feeding tray from a sheet supporting face to the separation nip portion is higher than the height in the conventional technique, on the upstream side of the separation nip portion.
In a sheet feeding tray configured to have a large height difference between the sheet supporting face and the separation nip portion, a distance between the sheet on the uppermost face of the sheet feeding tray and the separation nip portion becomes long when a small number of thin paper is stacked on the sheet feeding tray. Therefore, a sheet such as the thin paper having the low stiffness is likely to buckle at a position between the sheet feeding tray and the separation nip portion.
In order to solve the above problem, a swingable guiding member as described in Japanese Patent Application Laid-Open No. 2008-68968 may be employed. However, according to the configuration described in Japanese Patent Application Laid-Open No. 2008-68968, an angle between the swingable guiding member and a lower guide that faces the swingable guiding member will not be changed regardless of whether the sheets are fully stacked or the sheets of a small number are stacked thereon. Therefore, in a case where the angle between the swingable guiding member and the lower guide facing it, formed in a fully stacked state is set to be the appropriate angle, an abutting angle between a leading end of the sheet and the swingable guiding member, formed in the stacked state of a small number of sheets will be large.
Specifically, because a leading end of the sheet kept in a bookbinder as a file is likely to be warped upward, the abutting angle thereof will be larger. Therefore, there is a risk in which the sheet cannot be fed to the separation nip portion because the sheet cannot pass through a space between the swingable guiding member and the lower guide.